Does marathon running increase or decrease the risk of cardiac arrest?

Marathon running can increase your risk of cardiac arrest in the short term, but it also lowers the overall likelihood that you will experience cardiac arrest or other heart problems, according to science, statistics and sports cardiologists.

"In general, endurance exercise substantially reduces the risk that someone will develop heart disease," said Dr Paul D Thompson, emeritus chief of cardiology at Hartford Hospital in Connecticut and co-author of a three-volume textbook about sports cardiology.

Exercise does not prevent heart disease altogether, though, he said, and the hearts of marathon runners, like those of sedentary people, can harbour fatty plaques that can break free and block an artery, causing cardiac arrest.

Interestingly, the risks for runners are heightened by racing. According to most estimates, about 1 in 100,000 marathon runners will experience cardiac arrest as an adult, but the incidence almost doubles during a marathon to about 1 in 57,000 participants, presumably because the excitement and stress of racing place extra strain on the heart.

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Middle-aged male racers also seem to be the most vulnerable. Thompson was a co-author of a 2012 study that found that, between 2000 and 2010, 59 people racing a full- or half-marathon in the United States experienced a cardiac arrest. Of those, 51 were middle-aged men, almost all competing in the marathon.

Another 2012 study, using survey data from marathon medical directors, concluded that the overwhelming majority of cases of cardiac arrest during races involve middle-aged men, most of whom collapse in the final four miles of the course.

Still, while middle-aged male runners’ relative risk of a cardiac arrest rises while they are completing 26.2 miles compared to when they are not, their absolute risk of cardiac arrest, even then, remains reassuringly low, Thompson said.

And overall, running lowers people’s chances of ever developing or dying from heart problems. A 2014 study published in the Journal of the American College of Cardiology found that, no matter how often or infrequently runners trained and raced, they were about 45 per cent less likely than non-runners to die from heart disease.

Obviously, however, talk to your doctor if you are concerned about your heart health, Thompson said, especially if you notice symptoms such as chest pain, shortness of breath, numbness in your left shoulder or jaw, or unusual fatigue before, during or after a run or race.